1. Field of the Invention
The present invention relates to a tensioner that provides appropriate tension to a running chain, belt, or the like.
2. Description of the Related Art
It has been common practice to use a tensioner for maintaining appropriate tension in a chain or the like. For example, a known chain guide mechanism, which slidably guides a transmission chain, such as an endless roller chain passing over respective sprockets of a crankshaft and of a cam shaft inside an engine room, uses a tensioner to urge a tensioner lever in order to maintain appropriate tension of the chain or the like.
A known tensioner 510 used in such a chain guide mechanism includes, as shown in FIG. 8, a plunger 520 having a plunger hole 521 that is open on a rear side, a housing 530 having a plunger bore 531 that is open on a front side and accommodates the plunger 520, a main spring 560 that is accommodated inside an oil pressure chamber 511 formed between the plunger 520 and the plunger bore 531 such as to freely expand and contract and that urges the plunger 520 toward the front side, and a relief valve 540 that releases the oil inside the oil pressure chamber 511 to the outside of the plunger 520 when the oil pressure in the oil pressure chamber 511 rises (see, for example, Japanese Patent Application Laid-open No. 2001-12569).
In the tensioner 510 described in Japanese Patent Application Laid-open No. 2001-12569, as shown in FIG. 8, a pressure passage 524 communicating with the oil pressure chamber 511, an outlet port 523 connecting the pressure passage 524 with the outside of the plunger 520, and a spring accommodating chamber 525 formed on the front side of the pressure passage 524 are provided in the plunger bottom 522. A relief valve 540 is made up of a valve member 542 slidably fitted into the pressure passage 524, and a relief spring 543 disposed in the spring accommodating chamber 525 and urging the valve member 542 toward the oil pressure chamber 511.
In this tensioner 510, when the oil pressure in the oil pressure chamber 511 rises, the valve member 542 moves forward against the urging force of the relief spring 543 so that the pressure passage 524 communicates with the outlet port 523 and the oil is released from the outlet port 523.